A simplified diagrammatic representation of a disk drive, generally designated as 10, is illustrated in FIG. 1. The disk drive 10 includes a data storage disk 12 that is rotated by a spindle motor 14. The spindle motor 14 is mounted to a base plate 16. An actuator arm assembly 18 is also mounted to the base plate 16. The actuator arm assembly 18 includes a head 20 (or transducer) mounted to a flexure arm 22 which is attached to an actuator arm 24 that can rotate about a pivot bearing assembly 26.
The actuator arm assembly 18 also includes a voice coil motor (VCM) 28 which moves the head 20 relative to the disk 12. The spin motor 14, and actuator arm assembly 18 are coupled to a number of electronic circuits 30 mounted to a printed circuit board 32. The electronic circuits 30 can include, for example, a digital signal processor (DSP), a microprocessor-based controller and a random access memory (RAM) device. Although a single disk 12 is illustrated in FIG. 1, the disk drive 10 may instead include a plurality of disks. For example, FIG. 2 illustrates a disk stack 15 that includes a plurality of disks 12, each of which may have a pair of data storage surfaces 36. The disks 12 are mounted on a cylindrical shaft and are designed to rotate about axis 38. The spin motor 14 as mentioned above, rotates the disk stack 15.
Referring now to the illustration of FIGS. 1-3, the actuator arm assembly 18 includes a plurality of heads 20, each of which correspond to one of the disk surfaces 36. Each head 20 is mounted to a corresponding flexure arm 22 which is attached to a corresponding portion of the actuator arm 24 that can rotate about the pivot bearing assembly 26. The VCM 28 operates to move the actuator arm 24, and thus moves the heads 20 relative to their respective disk surfaces 36. The heads 20 are configured to fly adjacent to the disk surfaces 36 on air bearings.
FIG. 4 further illustrates one of the disks 12. Data is stored on the disk 12 within a number of concentric tracks 40 (or cylinders). Each track is divided into a plurality of radially extending sectors 42 on the disk 12. Each sector 42 is further divided into a servo sector 44 and a data sector 46. The servo sectors 44 of the disk 34 are used to, among other things, accurately position the head 20 so that data can be properly written onto and read from the disk 12. The data sectors 46 are where non-servo related data (i.e., user data) is stored and retrieved. Such data, upon proper conditions, may be overwritten.
To accurately write data to and read data from the data sectors 46 of the disk 12, it is desirable to maintain the head 20 at a relatively fixed position with respect to a centerline of a designated track 40 during writing and reading operations (called a track following operation). To assist in controlling the position of the head 20 relative to the tracks 40, the servo sectors 44 contain, among other things, servo information in the form of servo burst patterns that include one or more groups of servo bursts, as is well-known in the art.
Data is written on the disk 12 by the electronic circuits 30 generating a write current that is conducted through a coil in the head 20. In response to the write current, the head 20 generates a magnetic flux that writes (i.e., sets) a magnetic state of an adjacent area of the surface 36 of the disk 12. The direction of the write current is switched to cause a corresponding change in the written magnetic state. With the trend toward writing data at increasingly high data rates and with decreased gap between the head 20 and disk 12, it may become increasingly important to provide higher rates of control of the write current parameters.
Moreover, at high data rates, the magnetic field that may be generated in the disk media in response to the write current becomes limited by the switching speed of the write head structure. In particular, the write head switching speed may limit the magnetic field generated in the disk media at data rates exceeding 1.5 Gb/s, as shown in FIG. 5, which is a graph of the maximum effective field versus data rate. In order to overcome this limitation, it is known to increase the write current. For example, as shown in FIG. 6, an increase in write current Iw results an increase in the media magnetization at a 2 GHz switching speed.
FIG. 6 is a graph of media magnetization versus time for various write currents applied at a 2 GHz write cycle. For example, curve 61 corresponds to a write current of 60 mA, while curve 62 corresponds to a write current of 120 mA and curve 63 corresponds to a write current of 240 mA. In general, higher write currents may result in higher peak media magnetization as well as a steeper slope of the media magnetization curve. For example, in FIG. 6, the highest peak media magnetization occurs with the highest write current (240 mA). However, increased write currents may result in an increase in the effective magnetic write width (MWW) onto the disk media. Thus, increased write currents may increase the occurrence of adjacent track erasures. Increased write currents may also result in higher power consumption and/or excess heat generation in the disk drive.